Lanthanide dielectric with controlled interfaces

ABSTRACT

Methods and devices for a dielectric are provided. One method embodiment includes forming a passivation layer on a substrate, wherein the passivation layer contains a composition of silicon, oxygen, and nitrogen. The method also includes forming a lanthanide dielectric film on the passivation layer, and forming an encapsulation layer on the lanthanide dielectric film.

TECHNICAL FIELD

The present disclosure relates generally to semiconductor devices anddevice fabrication, and particularly to dielectric layers and theirmethod of fabrication.

BACKGROUND

Scaling dielectric layers, including silicon dioxide (SiO2) beyond 2 nmgives rise to large leakage current due to direct tunneling. Thus,alternative high-k dielectrics have been proposed. Generally, “high-K”refers to dielectric constants greater than that of SiO2 (K˜3.9). Asused herein, “high-K” will refer to dielectric constants greater than15, while “medium-K” will refer to dielectric constants betweenapproximately 4-15.

The common approach has involved amorphous materials with higherdielectric constants, such as hafnium or zirconium oxides (K˜20-25) andtheir silicates (K˜10-14). The former group (oxides) show poor thermalstability and undergo reinsulatorlization at modest temperature (>800C).The later (silicates) achieve higher thermal stability at the expense oflower dielectric constants. Both groups, in general, when used as a gatedielectric directly on a silicon substrate, exhibit high interface statedensity and consequently severe mobility degradation for a field effecttransistor (FET) device. Additionally, oxygen-vacancy induced defectscreate a high density of shallow traps introducing threshold instabilityand reliability concerns.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a high-k dielectric including a lanthanide insulatorfilm with controlled interfaces in accordance with one or moreembodiments of the present disclosure.

FIG. 1B illustrates an expanded view of a portion of FIG. 1A.

FIG. 2 illustrates a transistor having a lanthanide film with controlledinterfaces in accordance with one or more embodiments of the presentdisclosure.

FIG. 3 illustrates a capacitor having a lanthanide dielectric film withcontrolled interfaces in accordance with one or more embodiments of thepresent disclosure.

FIG. 4A illustrates a buried capacitor-type DRAM memory cell having alanthanide dielectric film with controlled interfaces in accordance withone or more embodiments of the present disclosure.

FIG. 4B illustrates a trenched capacitor-type DRAM memory cell having alanthanide insulator film with controlled interfaces in accordance withone or more embodiments of the present disclosure.

FIG. 5A illustrates a floating gate-type memory cell having a lanthanideinsulator film with controlled interfaces in accordance with one or moreembodiments of the present disclosure.

FIG. 5B illustrates an expanded view of the high k dielectricillustrated in FIG. 5A.

FIG. 6 illustrates a MOCVD/ALD reactor that can be used in accordancewith one or more embodiments of the present disclosure.

FIG. 7 illustrates an e-beam evaporation vessel that can be used inaccordance with one or more embodiments of the present disclosure.

FIG. 8 illustrates a flow diagram of elements for an embodiment of amethod to form a semiconductor device including a lanthanide insulatorfilm with controlled interfaces by liquid-injection metal organicchemical vapor deposition according to one or more embodiments of thepresent disclosure.

FIG. 9 illustrates transfer characteristics of a transistor formedaccording to one or more embodiments of the present disclosure.

DETAILED DESCRIPTION

Methods and devices for a high k dielectric with controlled interfacesare provided. One method embodiment includes forming a passivation layeron a substrate, wherein the passivation layer contains a composition ofsilicon, oxygen, and nitrogen. The method also includes forming alanthanide dielectric film on the passivation layer, and forming anencapsulation layer on the lanthanide dielectric film.

In the following detailed description of the present disclosure,reference is made to the accompanying drawings that form a part hereof,and in which is shown by way of illustration how one or more embodimentsof the disclosure may be practiced. These embodiments are described insufficient detail to enable those of ordinary skill in the art topractice the embodiments of this disclosure, and it is to be understoodthat other embodiments may be utilized and that process, electrical,and/or structural changes may be made without departing from the scopeof the present disclosure.

FIG. 1A illustrates, at 100, a high-k dielectric including a lanthanideinsulator film 106 with controlled interfaces 103 and 107 in accordancewith one or more embodiments of the present disclosure. A passivationlayer 104 is shown formed over a semiconductor substrate 102 wafer,e.g., silicon. A lanthanide dielectric film 106 is shown formed over thepassivation layer 104. An encapsulation layer 107 is shown formed overthe lanthanide dielectric layer 106. Interface 103 is illustrated as theinterface between the passivation layer 104 and the substrate 102. Themeans by which passivation layer 104 controls interface 103 will bedescribed below. Interface 107 is shown as the interface betweenlanthanide dielectric layer 106 and any additional layer which may beused above the dielectric, e.g., a gate electrode such as 214 in FIG. 2,as controlled by encapsulation layer 108. The means by whichencapsulation layer 108 controls interface 107 will be described below.

In one or more embodiments, semiconductor substrate 102 may be a siliconwafer, as understood by one of ordinary skill in the art. Passivationlayer 104 will be described in more detail in connection with FIG. 1Bbelow. One or more embodiments could be applicable to other high kinsulators including reactive metal oxides, silicates, aluminates,oxynitrides, composites, and laminates, which may react readily withsilicon and metals. As used herein, the term “lanthanide” refers to theelement lanthanum and other rare-earth metals, e.g., praseodymium,neodymium, samarium, gadolinium, dysprosium, and erbium. Embodiments arenot limited to the given examples of lanthanides. As used herein, theterm “lanthanide dielectric” refers to the combination of a member ofthe lanthanide family of metals with additional elements, e.g.,lanthanide oxides, lanthanide silicates, and lanthanide aluminates.Embodiments are not limited to the given examples of lanthanidedielectrics enumerated above.

In one or more embodiments, lanthanide dielectric film 106 can serve asa dielectric for a semiconductor. In some prior approaches, silicondioxide was used as a dielectric layer. However, scaling SiO2 beyond 2nm can give rise to large leakage currents due to direct tunnelingbetween the dielectric and the substrate. In some prior approaches,amorphous materials with higher dielectric constants have been suggestedas replacements for SiO2, such as hafnium or zirconium oxides and theirsilicates. The aforementioned oxides have dielectric constants betweenapproximately 20˜25, but can show poor thermal stability and undergorecrystalization at temperatures less than 800C. The aforementionedsilicates have lower dielectric constants (10˜14). Furthermore, both ofthe oxides and silicates, when used as dielectrics directly on siliconsubstrates, e.g., 102, can exhibit high interface state density andfixed charges, consequently creating severe mobility degradation andthreshold shift for field effect transistor (FET) devices. Additionally,oxygen-vacancy induced defects can create a high density of shallowtraps introducing threshold instability and reliability concerns.

Lanthanide insulator film 106 can be a lanthanide oxide, e.g., La2O3,Pr2O3, Nd2O3, Sm2O3, Gd2O3, Dy2O3, and Er2O3, which can exhibit a largeband gap, typically greater than 5 ev, with conduction band offset withsilicon greater than 2 ev. Such oxides can also exhibit greater thermalstability on silicon substrates, e.g., 102, compared to ZrO2 or HfO2.Lanthanide oxides can also have higher effective dielectric constantswhen normalized for a given leakage current density, and can havelattice parameter matching with silicon, which is conducive to epi-oxidegrowth deriving still higher dielectric constant values. Additionally,lanthanide oxides exhibit superior leakage characteristics. Lanthanidedielectric film 106 can also be formed as stable lanthanide silicatesand aluminates.

Some prior processing schemes for lanthanide dielectrics can result inuncontrollable formation of unwanted SiO2, silicates (SixMyOz), andaluminates (AlxMyOz) at the substrate interface 103, which can lower theeffective dielectric constant of the films, and can create an unwantedhigher fixed charge density. Furthermore, some prior processing schemescan result in interface densities greater than 1E12/cm² and negativefixed charge density resulting in poor FET device characteristics due toreduced carrier mobility. According to one or more embodiments of thepresent disclosure, tools including at least: liquid injectionmetalorganic chemical vapor deposition (MOCVD), hot-wall reducedpressure liquid-injection atomic layer deposition (ALD),ultra-high-vacuum molecular-beam epitaxy (MBE) using e-beam evaporation,and high vacuum sputtering can be used to form lanthanide dielectricfilm 106 as described below in connection with FIGS. 6 and 7.

The “equivalent oxide thickness” (EOT) measurement, sometimes simplycalled “oxide equivalent,” is a convenient measure of the relativecapacitance of any dielectric layer of a given thickness relative to thethickness that might be required if an SiO2 dielectric layer is employedin any given application. The EOT of a dielectric layer is calculated bydividing the physical thickness of the layer by its dielectric constantover that of the silicon dioxide. The dielectric constant of silicondioxide is about 4. In one or more embodiments of the presentdisclosure, lanthanide dielectric film 106 can be formed to a thicknessof approximately 5 nm˜10 nm with an EOT of approximately 1 nm˜2 nm.

Lanthanide oxides can readily absorb moisture. Oxygen and unwantedcontaminates can readily diffuse through such films at modesttemperature. To ensure integrity of post formation processing and tocontrol the interface 107 between the dielectric and an additional layersuch as a gate electrode, encapsulation layer 108 can be formed on topof the lanthanide dielctric film 106. In one or more embodiments,encapsulation layer 108 can help control interface 107 by forming astable compound such as silicate, oxynitride, or aluminate at theinterface 107 and by preventing reactivity with water for the lanthanidedielectric film 106. Encapsulation layer 108 can be formed to athickness, e.g., 0.5 nm˜2.0 nm over the dielectric. In one ore moreembodiments, encapsulation layer 108 can be silicon nitride (SiN),undoped polysilicon, titanium nitride (TiN), tantalum nitride (TaN),tungsten nitride (WN), or PrTixOy, for example. Encapsulation layer 108can be formed using tools including rapid thermal anneal (RTA) orin-situ deposition from a composite source by e-beam, sputtering, ALD,or MOCVD.

FIG. 1B illustrates an expanded view of a portion of FIG. 1A. FIG. 1Billustrates an expanded view of passivation layer 104. Lanthanidedielectric films, e.g., 106, can react with oxygen, —OH ions, andhydrogen. Such films can also form silicate layers at room temperatureeven under ultra-high vacuum conditions. Furthermore, both oxygen andsilicon can inter-diffuse in lanthanide dielectric films, e.g., 106.While a high density of interface states can be due to unsaturated bondsat the interface 103, high density of fixed charge and traps can beassociated with non-stoichiometric silicate or silicide formation andassociated defects. By incorporating passivation layer 104, theinterface 103 is stabilized and defect formation, as described above, isminimized.

An appropriate oxygen concentration and Si—O bond formation at theinterface 103 is required to overcome the abovementioned defects,without forming weaker Si—H bonds to quench interface states whileimproving interface 103 stability. Simultaneously, sufficient Si—N bondsestablished at or near the interface 103 can substantially passivatereactivity with oxygen, —OH, and hydrogen.

As shown in the embodiment illustrated in FIG. 1B, passivation layer 104can include a nitride 112 formed above a composition of silicon, oxygen,and nitrogen “SiON” 110. In one or more embodiments, SiON layer 110 caninclude a mixture of approximately 40 atomic percent of oxygen, 20atomic percent of nitrogen, and 40 atomic percent of silicon. SiON layer110 can be formed to a thickness of 0.5 nm˜2.0 nm using tools such asliquid injection MOCVD, liquid injection ALD, or hot-wall reducedpressure liquid injection ALD. Formation methods will be described inmore detail below in connection with FIGS. 6 and 7.

In one or more embodiments, passivation layer 104 can be formed as twolayers, e.g., a bottom layer 110 formed on the substrate 102 and a toplayer 112 formed on the bottom layer 110. In one or more embodiments,top layer 112 can be formed as a nitride or a nitrogen rich oxy-nitride.Embodiments are not limited to a two layer passivation layer 104. Inembodiments including only a one-layer passivation layer 104, it can beformed substantially as described for bottom layer 110, e.g., SiON.Embodiments having a two-layered encapsulation layer 108 can include abottom layer formed to approximately 1.0 nm˜1.5 nm, and a top layerformed to approximately 0.5 nm˜1.0 nm.

FIG. 2 illustrates a transistor 200 having a lanthanide dielectric film206 with controlled interfaces 203 and 207 in accordance with one ormore embodiments of the present disclosure. In one or more embodiments,transistor 200 can be a field effect transistor (FET). As will beappreciated by one of ordinary skill in the art, the transistor 200 canbe used as a basic high performance device for logic circuits such asmicroprocessors as well as in a semiconductor memory cell, for example,in a DRAM as described in connection with FIGS. 4A and 4B, or anon-volatile memory cell as described in connection with FIGS. 5A and5B.

Diffusion regions 216, e.g., a source region and a drain region, can beformed in substrate, e.g., silicon semiconductor substrate wafer, 202. Apassivation layer 204 may be formed on the substrate 202. A lanthanidedielectric film dielectric 206 may be formed on the passivation layer204. An encapsulation layer 208 may be formed on the lanthanidedielectric film 206. A gate electrode 214 may be formed on theencapsulation layer 208.

The passivation layer 204, lanthanide dielectric film 206, andencapsulation layer 208 may be formed and may function substantially asdescribed in connection with FIGS. 1A, 1B, 6, and 7. Furthermore,controlled interfaces 203 and 207 are substantially similar tocontrolled interfaces 103 and 107 as described in connection with FIG.1A. Gate electrode 214 can be used to apply a voltage to the transistor200 in order to create a conductive channel in the substrate 202 betweenthe diffusion regions 216. Transistor 200 can be a metal oxidesemiconductor (MOS) transistor.

In one or more embodiments, the lanthanide dielectric film 206 may beformed as a lanthanide silicate, lanthanide aluminate, stablepolycrystal lanthanide oxide, amorphous lanthanide oxide, stablemono-crystalline oxide, or an amorphous or stable mono-crystallinealuminate, for example. The dielectric constant for the lanthanidedielectric layer 206 may be greater than 20. The EOT for the transistor200 may be approximately 1.0 nm˜1.5 nm. According to one or moreembodiments of the present disclosure, the effective electron mobilityfor the transistor may be greater than 500 cm²/V-sec. In one or moreembodiments, the transistor may have a sub-Vt slope of approximately 80mV/dec and a Vth of approximately 0.5V, as described in more detail inconnection with FIG. 9. The transistor 200 provides the building blockfor high performance future generation logic circuits such as can beemployed in high performance microprocessors.

FIG. 3 illustrates a capacitor 300 having a lanthanide dielectric film306 with controlled interfaces 305 in accordance with one or moreembodiments of the present disclosure. In one or more embodiments,capacitor 300 can be formed on substrate 302. As will be appreciated byone of ordinary skill in the art, the capacitor 300 can be used in asemiconductor memory cell, for example, in a DRAM as described inconnection with FIGS. 4A and 4B. Alternatively, the capacitor 300 canalso be used as a discrete capacitor element in logic and RF circuits.The capacitor 300 includes conductive electrode layers 318, which can beformed from conductive materials such as metals, polysilicon, or dopedpolysilicon.

As shown in the embodiment illustrated in FIG. 3, capacitor 300 includespassivating layers 309 between and adjacent to the conductive layers318. In one or more embodiments, passivating layers can be formed asTiN, TaN, or WN. As is also shown in the embodiment illustrated in FIG.3, capacitor 300 includes a lanthanide dielectric film 306 between theencapsulating layers. Lanthanide dielectric film 306 also can be formedas materials described above in connection with FIG. 1A. In one or moreembodiments, lanthanide dielectric film 306 can be formed as a two-layerdielectric including a layer of PrTiOx and a layer of PrSiOx. Therelative position of the layers of PrTiOx and PrSiOx can be reversed inone or more embodiments. The order of placement of the layers depends onthe particular fabrication process for the device and relative positionof the layers with respect to the electrode material selections andintegration requirements.

Capacitors 300 formed according to one or more embodiments of thepresent disclosure can provide as much as double capacitor storagecapacity compared to capacitors formed using Al2O3, HfO2, or ZrO2dielectric layers. Capacitors 300 can achieve dielectric constants of 22or greater for structures including passivating layer-lanthanidedielectric film-passivating layer (309-306-309). Such as structuresincluding TiN—PrSiOx—TiN, TiN—PrTiOx—TiN, TiN—PrTiOx/PrSiOx—TiN,TaN—PrTiOx/PrSiOx—TaN, and WN—PrTiOx/PrSiOx—WN, and other similarcombinations of lanthanum family dielectrics. Capacitors 300 formedaccording to one or more embodiments of the present disclosure canachieve dielectric constants of 30 for structures including singledielectric Pr2O3 as the lanthanide dielectric film 306.

FIG. 4A illustrates a buried capacitor-type DRAM memory cell 400-Ahaving a lanthanide dielectric film 406 with controlled interfaces 403,405, and 407 in accordance with one or more embodiments of the presentdisclosure. FIG. 4B illustrates a trenched capacitor-type DRAM memorycell 400-B having a lanthanide dielectric film 406 with controlledinterfaces 403 and 407 in accordance with one or more embodiments of thepresent disclosure. The details of controlled interfaces 403 and 407 aresubstantially the same as described above in connection with FIG. 1A forinterfaces 103 and 107. The one or more embodiments illustrated in FIGS.4A and 4B can be used in DRAM memory cells.

FIGS. 4A and 4B include capacitors 430 including storage electrodes 432and plate electrodes 434. Storage electrodes 432 and plate electrodes434 can be made of any conductive or semiconductive material asrepresented by conductive layer 318 in FIG. 3. In one or moreembodiments, storage electrodes 432 and plate electrodes 434 are made ofpolycrystalline or crystalline silicon, a refractory metal such as W,Mo, Ta, Ti or Cr, or combinations thereof such as WSi2, MoSi2, TaSi2 orTiSi2. It will be appreciated that the electrodes 432 and 434 may bemade from other materials without departing from the scope of thepresent disclosure. In one or more embodiments, storage electrodes 432and plate electrodes 434 are separated by passivating layers 409, e.g.,309 in FIG. 3, with controlled interfaces 405, e.g., 305 in FIG. 3, anda lanthanide dielectric film 406, e.g., 306 in FIG. 3.

The capacitors 430 are used to store charge representing data. Access tothe capacitors 430 is made via a select line, e.g., word line, 422 andsense line, e.g., bit line, 424. The select lines 422 are the gateelectrodes, e.g., 214 in FIG. 2, of the transistors 420 that are used toform a conductive channel between diffusion regions, e.g., source/drainregions, 416, e.g., 216 in FIG. 2, when sufficient voltage is applied tothe select line 422. In one or more embodiments of the presentdisclosure, the select line 422 is located above encapsulation layers408. As described above in connection with FIG. 1A, encapsulation layers408, e.g., 108 in FIG. 1A, can be formed as silicon nitride (SiN),undoped polysilicon, titanium nitride (TiN), tantaium nitride (TaN),tungsten nitride (WN), or PrTixOy.

In the one or more embodiments illustrated in FIGS. 4A and 4B,encapsulation layers 408 are located above lanthanide dielectric films406. As described above in connection with FIG. 1A, lanthanidedielectric films 406, e.g., 106 in FIG. 1A, can be formed as lanthanidesilicates, lanthanide aluminates, stable polycrystal lanthanide oxides,amorphous lanthanide oxides, stable mono-dielectricline oxides, andstable amorphous or mono-crystalline aluminates. The lanthanidedielectric films used as dielectrics for the transistors 420 andcapacitors 430 can be made from the same, or different, materials for aparticular DRAM device.

As is also illustrated in the one or more embodiments illustrated inFIGS. 4A and 4B, lanthanide dielectric films 406 are located abovepassivation layers 404, which are located above substrate 402. Asdescribed above in connection with FIG. 1, passivation layers 404, e.g.,104 in FIG. 1A, can be formed as a composition of silicon, oxygen, andnitrogen. In one or more embodiments the composition can include 40atomic percent of oxygen, 20 atomic percent of nitrogen, and 40 atomicpercent of silicon. As is also described above in connection with FIG.1B, in one or more embodiments, passivation layer 404 can be formed as alayer of SiON and a layer of nitride or nitrogen rich oxy-nitride, e.g.,layers 110 and 112 respectively in FIG. 1B. Formation processes for thevarious layers illustrated in FIGS. 4A and 4B are described in moredetail below in connection with FIGS. 6 and 7.

FIG. 5A illustrates a floating gate-type memory cell 500 having alanthanide dielectric film with controlled interfaces in accordance withone or more embodiments of the present disclosure. Transistor 500includes a substrate 502, e.g., a silicon based substrate, withdiffusion regions 516, e.g., a source and a drain. In one ore moreembodiments, the substrate 502 can be a p-type silicon substrateimplanted with n-type diffusion regions 516. In one or more embodiments,the substrate 502 can be an n-type silicon substrate implanted withp-type diffusion regions 516.

Located above substrate 502 is a stack including a tunnel dielectric548, a floating gate (FG) 544, a charge blocking dielectric 546, acontrol gate (CG) 542, and a select line, e.g., word line, contact 540.Floating gate 544 can be used to store charge representing data.Although not shown in FIG. 5A, the select line connected to select linecontact 540 continues to connect each of the control gates of othermemory cells, e.g., transistors on the select line running in and/or outof the page, as illustrated in FIG. 5A. Both dielectric layers 548 and546 can be high k lanthanide dielectric films as illustrated in FIG. 5B.

FIG. 5B illustrates an expanded view 548 of the high k dielectricillustrated in FIG. 5A. FIG. 5B includes a passivation layer 504, alanthanide dielectric film 506, an encapsulation layer 508, andcontrolled interfaces 503 and 507. Passivation layer 504 is formed onsubstrate 502, as illustrated in FIG. 5A. Floating gate 544 in FIG. 5Ais formed over encapsulation layer 508, illustrated in FIG. 5B. Elementsof FIG. 5B can be formed substantially as described above in connectionwith FIGS. 1A and 1B and as described below in connection with FIGS. 6and 7.

As one of ordinary skill in the art will appreciate, charge blockingdielectric 546 in FIG. 5A could also include a passivation layer, e.g.,504 in FIG. 5B, and/or an encapsulation layer, e.g., 508 in FIG. 5B.Transistor 500, illustrated in FIGS. 5A and 5B, can be a non-volatilememory cell, such as is commonly used in a NAND or NOR flash array.

FIG. 6 illustrates a MOCVD/ALD reactor 600 that can be used inaccordance with one or more embodiments of the present disclosure. Theelements depicted permit discussion of the present disclosure such thatthose skilled in the art may practice the present invention withoutundue experimentation. In FIG. 6, a target 656, e.g., substrate, can belocated inside a reaction chamber 684 of MOCVD/ALD reactor 600. Alsolocated within the reaction chamber 684 can be a heated rotary stage654, which can be thermally coupled to target 656 to control the targettemperature. A vaporizer 658 can introduce precursors to the target 656.Each precursor can originate from sources 660, including sources 662,664, and 666, whose flow can be controlled by mass-flow controllers 680.Sources 660 can provide precursors by providing a liquid material toform the selected precursor gas in vaporizer 658.

Also included in the MOCVD/ALD reactor 600 can be purging gas sources670 including 672 and 674. Furthermore, additional purging gas sourcescan be constructed in MOCVD/ALD reactor 600, one purging gas source foreach precursor gas, for example. For a process that uses the samepurging gas for multiple precursor gases less purging gas sources arerequired for MOCVD/ALD system 600. The MOCVD/ALD reactor 600 also caninclude gas sources 676, 678, and 679 for introduction to reactionchamber 684 without needing to be vaporized at 658 for ALD modeoperation. Reaction chamber 684 also can be coupled to vacuum pump, orexhaust pump, 652, after thermocouple 650, to remove excess precursorgases, purging gases, and by-product gases at the end of a purgingsequence from the reaction chamber 684.

For convenience, control displays, mounting apparatus, temperaturesensing devices, substrate maneuvering apparatus, and necessaryelectrical connections as are known to those skilled in the art are notshown in FIG. 6. Though MOCVD/ALD reactor 600 is well suited forpracticing the present invention, other MOCVD/ALD systems commerciallyavailable can be used.

The use, construction and fundamental operation of reaction chambers fordeposition of films are understood by those of ordinary skill in the artof semiconductor fabrication. The present invention may be practiced ona variety of such reaction chambers without undue experimentation.Furthermore, one of ordinary skill in the art will comprehend thenecessary detection, measurement, and control techniques in the art ofsemiconductor fabrication upon reading the present disclosure.

The elements of MOCVD/ALD reactor 600 can be controlled by a computer.To focus on the use of MOCVD/ALD reactor 600 in the various embodimentsof the present invention, the computer is not shown. Those skilled inthe art can appreciate that the individual elements such as pressurecontrol, temperature control, and gas flow within MOCVD/ALD system 600can be under computer control.

MOCVD/ALD reactor 600 can be used to form a passivation layer, e.g., 104as described above in connection with FIGS. 1A and 1B. A passivationlayer, e.g., passivation layer 104, including 40 atomic percent ofoxygen, 20 atomic percent of nitrogen, and 40 atomic percent of silicon,with a refractive index of approximately 1.6, could be deposited to athickness of approximately 1 nm˜2 nm over a silicon substrate, e.g.,target 656. In one or more embodiments, formation could be performedafter some preliminary steps. For example, appropriate high temperaturedegassing of the reaction chamber 684, e.g., pre-baking at 450C in anultra-pure nitrogen environment to help provide complete desorption ofhydrogen and moisture from silicon surface and a contamination freesilicon surface prior to SiON deposition. Furthermore, pre-cleaning ofsubstrate, e.g., target 656, interface oxidation, e.g., interface 103 inFIG. 1A, and in-situ vapor-phase removal of native oxide from thesurface of the silicon substrate, e.g., target 656 can be performedprior to formation.

An SiON passivation layer, e.g., 104 in FIGS. 1A and 1B, can bedeposited in MOCVD mode using reactants SiCl4, NH3, N2O, or ozoneappropriately diluted in a nitrogen carrier at approximately 650C˜750C.Such a layer could also be formed in ALD mode with cycles of SiCl4 atapproximately 400C˜450C and NH3—N2O—N2 or NH3—O3—N2 at approximately650C˜700C while maintaining appropriate gas pressures of SiCl4, NH3, andN2O to achieve desired film composition at a slow deposition rate lessthan 0.1 nm/sec.

As described above in connection with FIG. 1B, the passivation layercould also be formed of a bottom layer of SiON, e.g., 110 in FIG. 1B,and a top layer of nitride or nitrogen-rich SiON, e.g., 112 in FIG. 1B.In one or more embodiments utilizing a two-layer passivation layer, asdescribed in connection with FIG. 1B, the layer of nitride could beformed to a thickness of approximately 0.5 nm˜1.0 nm. A layer ofnitrogen-rich SiON, having a refractive index of approximately 1.8,could be formed by appropriately controlling the N2O content. A layer ofnitride, having a refractive index of approximately 2.0, could be formedby eliminating N2O altogether during deposition of the nitride layer.

Cyrstallography, film composition and quality, and electricalcharacteristics of lanthanide dielectrics are very sensitive tosubstrate, e.g., 102 in FIG. 1A, preparation and interface, e.g., 103 inFIG. 1A, passivation. Formation of lanthanide dielectrics is also verydependent on source material composition and preparation, temperature ofdeposition, and ambient conditions. Generally, oxide films grown by ALDor MOCVD at substrate temperatures below 650C are polydielectricline,e.g., hexagonal and oxygen-rich, with or without an amorphous silicateinterlayer when tetramethylheptanedionate [(tmhd)3] andmethoxymethlypropanolate [(mmp)3] precursor family of source materialsare used. These films are characteristically textured and exhibit poorerelectrical characteristics and undergo structural changes when annealedabove 800C. Films grown at higher temperatures are relatively morestable on annealing in inert ambient, e.g., Ar or N2, and the silicateinterlayer may undergo dielectriclization in an oxygen environment. Incontrast, silicates are more stable and remain amorphous even whendeposited by ALD or MOCVD means at substrate, e.g., target 656, attemperatures between approximately 250C˜550C when silylamide precursorsources are used.

After the passivation layer, e.g., 104 in FIG. 1A, is formed asdescribed above, a lanthanide dielectric film, e.g., 106 in FIG. 1A, canbe formed using MOCVD/ALD reactor 600. Lanthanide silicates can beformed in MOCVD mode using a source material of [Ln{n(SiMe3)2}3](lanthanide trialkyl silylamide) in toluene with tetraglyme added forstabilization, and held at approximately 170C with carrier gasconsisting of either argon+N2O or nitrogen+N2O. The substratetemperature can be held around 400C˜600C and the reactor pressure can beheld at approximately 1 mbar. Incorporation of N2O can help ensureremoval of carbon from the film by forming volatile CO2while keeping thepartial pressure of oxygen appropriate for the silicate film formed. Thegrowth rate can be approximately 5 nm˜7 nm/min. Lanthanide silicate canbe deposited in the range of approximately 5 nm˜10 nm with an EOT ofapproximately 1 nm˜2 nm. The particular lanthanides formed can includeLa, Pr, or Gd, using the above conditions.

Lanthanide silicates can be formed in ALD mode by keeping reactor 600and above mentioned sources the same except for the following changes.The carrier gas can be argon+O3 or nitrogen+O3. The substratetemperature can be held around 200C˜400C while the precursor pulselength can be approximately 0.5˜1.0 sec. In one or more embodiments amixture of water vapor and ozone can be employed to control thedeposition rate along with nitrogen or argon. A precursor volume ofapproximately 20 μL-40 μL per cycle can be employed.

Lanthanide aluminates can be formed in MOCVD or ALD mode substantiallyas described above, but by using precursors including lanthanideamidinates [Ln(R—NCHN—R)3] in combination with Me3Al.

In order to help reduce the poorer structural stability and electricalcharacteristics of lanthanide-oxide polycrystalline structures resultingfrom MOCVD/ALD reactions using Ln(mmp)3 and Ln(mthd)3 families ofprecursors, excess silicon can be incorporated during deposition todrive the surface reaction towards silicate formation around the grainboundaries. This can be achieved by substantially simultaneouslyincorporating SiCl4 and {Ln(mmp)3 or Ln(mthd)3 or sylilamide} precursorsat the substrate. This can result in a mixed oxide/silicate amorphousfilm that can enhance thermal stability and electrical properties. Usinga Gd(mmp)3 precursor deposited over a silicon substrate at a temperaturegreater than 450C in the absence of oxygen can result in single-crystalstable Gd2O3 film. At lower temperatures and in the presence of oxygen,the film can be amorphous.

An encapsulation layer, e.g., 108 in FIG. 1A, can be formed on thelanthanide dielectric layer, e.g., 106 in FIG. 1A. An encapsulationlayer can help passivate the film at the interface, e.g., 107 in FIG.1A, and protect against post-processing contaminants throughout anintegration process. An in-situ deposition of approximately 0.5˜2.0 nmthick SiN film can help encapsulate the dielectric layer with only aslight reduction in the effective dielectric constant. Other options foran encapsulation layer include undoped polysilicon, TiN, TaN, or WN.Such a layer could be deposited by standard in-situ CVD and othertechniques. Optimum encapsulation layers for a given dielectric layermay be selected by one of ordinary skill in the art. For example, TiNcan be an effective interface layer in preventing silicate formation andreactivity with water for Pr2O3 as a dielectric film.

FIG. 7 illustrates an e-beam evaporation vessel 700 that can be used inaccordance with one or more embodiments of the present disclosure. Thee-beam evaporation vessel 700 can be located on top of a base plate 781.The substrate, e.g., target 756, can include a previously depositedpassivation layer of SiON and/or (nitrogen-rich) nitride. The substrate,e.g., target 756, can be held in a substrate support device 788 with thetarget surface facing a shutter 786 that controls exposure of thesubstrate surface to the beam of evaporated lanthanide source 706. Thebeam can be emitted by bombardment from an electron gun 790 situated inthe lower part of the chamber below the shutter 786.

The temperature of the substrate, e.g., target 756, and chamberenvironment can be controlled by a heater 787 assembly that may includean optional reflector 789 in proximity to the substrate, e.g., target756. An oxygen distribution ring 783 can be located below the shutter786. The oxygen distribution ring can be a manifold that distributesoxygen around the surface of the substrate, e.g., target 756, at apressure of about 1 E-7 Torr. The electron beam evaporation vessel 700can be configured with a vacuum pump 752 for evacuating the chamber to apressure of about 10 E-6 Torr or less. Oxygen pressure in the chambercan be regulated by oxygen control regulator 780. A small amount ofoxygen is needed in the chamber to ensure that the deposited layer oflanthanide film is completely oxidized because the process of e-beamevaporation tends to degrade the oxidation stoichiometry of thelanthanide material 706. Optional detectors or monitors may be includedon the interior or exterior of the vessel 700, such as an interiorlysituated detector 791 for detecting the thickness of the layer and theexteriorly situated monitor 792 for displaying the thickness of thelayer. The lanthanide dielectric layer can be formed to a suitablethickness of approximately 5 nm˜10 nm with an EOT of approximately 1nm˜2 nm by controlling the duration of electron beam evaporation.

Using the process scheme described above, an approximately 2 nm thickstable silicate interface layer may be formed under ultra-high vacuumconditions for Pr2O3 single-dielectric formation on a silicon substrateat approximately 600C. Optionally, stable Pr-silicate (PrSixOy)amorphous films can also be deposited at lower substrate temperatures,which can achieve dielectric constants of approximately 22.

Stable mono-crystalline Pr2O3 can be deposited over silicon substrate,e.g., target 756, using e-beam evaporation from solid single crystalpallets of Pr6O11 crystals at 706. Following the formation of apassivation layer, e.g., 104 in FIG. 1A, as described above,single-crystal Pr2O3 films could be deposited without a silicateinterface layer. An undoped polysilicon layer of approximately 100 nmthickness can be deposited in-situ to eliminate moisture absorptionprior to subsequent processing. For other lanthanide oxide dielectricfilms, a similar approach could be employed using other LnOx material asa source, as will be understood by one of ordinary skill in the art.Alternatively, for single-crystal aluminate films, single-crystal LnAlO3could be used as targets and laser sputter deposition techniques couldbe employed at around 1 E-7 Torr at a substrate temperature ofapproximately 650C˜700C.

FIG. 8 illustrates a flow diagram 800 of elements for an embodiment of amethod to form a semiconductor device including a lanthanide dielectricfilm with controlled interfaces by liquid-injection metal organicchemical vapor deposition according to one or more embodiments of thepresent disclosure. Elements 810, 820, 830, 840, 850, and 860 indicategeneral elements of a method to form a semiconductor device. Elementsreflect sub-elements of the general element from which they flow. Forexample, 811, 813, 815, and 817 provide more detail about generalelement 810.

At 810, a silicon substrate, e.g., 102 in FIG. 1A, can be pre-cleaned,the surface can be oxidized, and annealed. Element 810 includes an RCAclean and 5% HF dip to remove hydrated oxide from the substrate at 811.At 813, a low temperature ozone oxidation can be used to form aprotective oxide at 600C. At 815, an in-situ HF-vapor clean can beperformed to achieve a clean silicon surface free from oxide. At 817,the substrate can be UV-baked to help ensure a clean silicon substratesurface and remove hydrogen from the interface, e.g., interface 103 inFIG. 1A.

At 820, a SiON passivation layer can be deposited to a thickness ofapproximately 0.5 nm˜1.0 nm as described in more detail with respect toFIGS. 1A, 1B, and 6. Element 820 can include the use of precursorsSiCl4, NH3, N2O, and N2 at 700C at 821. At 823, a programmed reductionof N2O flow can be used to convert a top layer of the overallpassivation layer into a nitride or a nitrogen-rich nitride, e.g., 812in FIG. 1B. As described in connection with FIGS. 1A and 1B, passivationlayer 104 can include either a single layer of SiON, or two layersincluding a bottom layer 110 of SiON and a top layer 112 of nitride ornitrogen-rich nitride.

At 830 a lanthanide dielectric film, e.g., 106 in FIG. 1A, e.g.,Ln-silicate, can be in-situ deposited to a thickness of approximately 4nm˜5 nm. Element 830 can include the use of precursors SiCl3,Pr-trialkyl silylamide, ozone, and (N2 or Ar) at a temperature ofapproximately 500C˜550C with a growth rate of approximately 5 nm/min ata pressure of 1 mbar at 831. Formation of this layer is described inmore detail with respect to FIGS. 6 and 7.

At 840, an encapsulation layer, e.g., 108 in FIG. 1A, e.g., SiN, isin-situ deposited to a thickness of approximately 0.5 nm˜1.0 nm. Element840 can include the use of precursors SiCl4, NH3, and N2 atapproximately 700C at 841. Formation of this layer is described in moredetail with respect to FIGS. 6 and 7.

At 850, an ex-situ RTA anneal in N2 at 900C can be performed on thesubstrate, e.g., 102 in FIG. 1A. At this point, the substrate caninclude a passivation layer, a lanthanide dielectric film, and anencapsulation layer. As one of ordinary skill in the art willappreciate, elements 815 through 850 could be performed in onecontrolled environment, without removing the substrate betweenprocesses, for ease of processing. At 860, standard post processing canoccur, as will be understood by one of ordinary skill in the art.

FIG. 9 illustrates transfer characteristics of a transistor formedaccording to one or more embodiments of the present disclosure. Thex-axis is a linear representation of gate voltage, measured in volts.The y-axis is a logarithmic representation of drain current over channelwidth measured in amps/μm. In the embodiment illustrated in FIG. 9, thetransistor can be formed including a lanthanide dielectric film, e.g.,106 in FIG. 1A, including Pr2O3 as the lanthanide dielectric, forexample. The channel width can be approximately 100 μm for the exampleillustrated in FIG. 9.

Element 900-1 represents the transfer characteristics for a deviceformed according to some prior approaches, e.g., without interfacecontrol. Element 900-1 illustrates a sub-threshold Vt shift of 145mV/decade. Element 900-2 represents the transfer characteristics for adevice formed according to one or more embodiments of the presentdisclosure using interface control. Element 900-2 illustrates asub-threshold Vt shift of 80 mV/decade. The significantly highersub-threshold Vt shift illustrated at 900-1, without interface control,can indicate that the device turns on, e.g., conducts slowly in responseto an applied gate potential due to poor interface characteristics.Nearly ideal device characteristics with superior speed and leakage areachieved with interface control as illustrated at 900-2.

Conclusion

Methods and devices for a dielectric with controlled interfaces areprovided. One method embodiment includes forming a passivation layer ona substrate, wherein the passivation layer contains a composition ofsilicon, oxygen, and nitrogen. The method also includes forming alanthanide dielectric film on the passivation layer, and forming anencapsulation layer on the lanthanide dielectric film.

Although specific embodiments have been illustrated and describedherein, those of ordinary skill in the art will appreciate that anarrangement calculated to achieve the same results can be substitutedfor the specific embodiments shown. This disclosure is intended to coveradaptations or variations of various embodiments of the presentdisclosure. It is to be understood that the above description has beenmade in an illustrative fashion, and not a restrictive one. Combinationof the above embodiments, and other embodiments not specificallydescribed herein will be apparent to those of skill in the art uponreviewing the above description. The scope of the various embodiments ofthe present disclosure includes other applications in which the abovestructures and methods are used. Therefore, the scope of variousembodiments of the present disclosure should be determined withreference to the appended claims, along with the full range ofequivalents to which such claims are entitled.

In the foregoing Detailed Description, various features are groupedtogether in a single embodiment for the purpose of streamlining thedisclosure. This method of disclosure is not to be interpreted asreflecting an intention that the disclosed embodiments of the presentdisclosure have to use more features than are expressly recited in eachclaim. Rather, as the following claims reflect, inventive subject matterlies in less than all features of a single disclosed embodiment. Thus,the following claims are hereby incorporated into the DetailedDescription, with each claim standing on its own as a separateembodiment.

1. A method of forming a high-k dielectric with controlled interfaces,comprising: forming a passivation layer on a substrate, wherein thepassivation layer contains a composition of silicon, oxygen, andnitrogen; forming a lanthanide dielectric film on the passivation layer;and forming an encapsulation layer on the lanthanide dielectric film. 2.The method of claim 1, wherein the method includes forming thepassivation layer over the substrate to a thickness of approximately 0.5nm-2.0 nm.
 3. The method of claim 1, wherein forming the passivationlayer includes: forming a bottom layer on the substrate, wherein thebottom layer includes approximately 40 atomic percent of oxygen, 20atomic percent of nitrogen, and 40 atomic percent of silicon; andforming a top layer on the bottom layer, wherein the top layer isselected from the group including: nitrogen rich nitride; and nitride.4. The method of claim 1, wherein forming the lanthanide dielectric filmincludes a lanthanide dielectric selected from the group including:lanthanide silicates; lanthanide aluminates. stable polycrystallanthanide oxides; amorphous lanthanide oxides; stable mono-crystallineoxides; and stable mono-crystalline aluminates.
 5. The method of claim1, wherein the method includes forming the lanthanide dielectric film toa thickness of approximately 5 nm-10 nm with an effective oxidethickness (EOT) of approximately 1 nm-2 nm.
 6. The method of claim 1,wherein the method includes forming the encapsulation layer selectedfrom the group including: silicon nitride (SiN); titanium nitride (TiN);tantaium nitride (TaN); tungsten nitride (WN); undoped polysilicon; andPrTixOy.
 7. A method of forming a high-k dielectric with controlledinterfaces, comprising: pre-cleaning a substrate; pre-baking thesubstrate at a temperature greater than 450C in a nitrogen environment;forming a passivation layer on the substrate, wherein the passivationlayer includes approximately 40 atomic percent of oxygen, 20 atomicpercent of nitrogen, and 40 atomic percent of silicon; forming alanthanide dielectric film on the passivation layer; and forming anencapsulation layer on the lanthanide dielectric film.
 8. The method ofclaim 7, wherein the method includes using chemical vapor deposition(CVD) to form the passivation layer by reacting SiCl4, NH3, and N2O in anitrogen carrier at approximately 650C-700C.
 9. The method of claim 7,wherein the method includes using atomic layer deposition (ALD) to formthe passivation layer by cycling SiCl4 at approximately 400C-450C andNH3—N2O—N2 at approximately 650C-700C.
 10. The method of claim 7,wherein the method includes using metalorganic chemical vapor deposition(MOCVD) to form the lanthanide dielectric film, and wherein using MOCVDincludes: holding the substrate at approximately 400C-600C; and using acarrier gas selected from the group including: argon+N2O; andnitrogen+N2O.
 11. The method of claim 7, wherein the method includesusing atomic layer deposition (ALD) to form the lanthanide dielectricfilm, and wherein using ALD includes: holding the substrate atapproximately 200C-400C; using a precursor pulse length of approximately0.5 sec-1.0 sec; using a precursor volume of approximately 20 μL-40 μLper cycle; and using a carrier gas selected from the group including:argon+ozone; and nitrogen+ozone.
 12. The method of claim 7, whereinforming the lanthanide dielectric film includes forming lanthanidesilicates by injecting lanthanide trialkyl silylamide [Ln{n(SiMe3)2}3]in toluene with tetraglyme as the at least one precursor.
 13. The methodof claim 7, wherein forming the lanthanide dielectric film includesforming lanthanide aluminates by injecting lanthanide amidinates[Ln(R—NCHN—R)3] with Me3Al as the at least one precursor.
 14. The methodof claim 7, wherein forming the lanthanide dielectric film includesusing metalorganic chemical vapor deposition (MOCVD) to form anamorphous lanthanide mixed oxide/silicate film by injecting SiCl4 and anadditional precursor selected from the group including: lanthanidemethoxymethylpropanolate [Ln(mmp)3]; lanthanidemethoxytetraethylheptanedionate [Ln(mthd)3]; and silylamide.
 15. Themethod of claim 7, wherein forming the lanthanide dielectric filmincludes forming a stable mono-dielectricline Gd2O3 film by depositingSiCl4 and Gd(mmp)3 precursors over the substrate in the absence ofoxygen and at a temperature greater than 450C.
 16. A semiconductortransistor, comprising: a substrate; a source region and a drain region;a passivation layer on the substrate, bridging the source region anddrain region; a lanthanide dielectric layer on the passivation layer; anencapsulation layer on the lanthanide dielectric layer; and a gateelectrode on the encapsulation layer; wherein a dielectric constant (K)for the lanthanide dielectric layer is greater than
 20. 17. Thetransistor of claim 16, wherein the passivation layer functions topassivate against: interface states generation; fixed charge generation;and SiO2 and silicide formation at an interface between the substrateand the lanthanide dielectric.
 18. The transistor of claim 16, whereinan effective oxide thickness (EOT) for the transistor is approximately1.5 nm.
 19. The transistor of claim 16, wherein an effective electronmobility for the transistor is greater than 500 cm²/V-sec.
 20. Thetransistor of claim 16, wherein a sub-Vt slope for the transistor isapproximately 80 mV/dec.
 21. The transistor of claim 16, wherein Vth forthe transistor is approximately 0.5V.
 22. A semiconductor capacitor,comprising: a first conductive layer; a first passivating layer on thefirst conductive layer; a dielectric layer, including a lanthanidedielectric film, on the first encapsulating layer; a second passivatinglayer on the lanthanide dielectric film; a second conductive layer onthe second passivating layer; and wherein, a dielectric constant (K) forthe lanthanide dielectric layer is greater than
 20. 23. The capacitor ofclaim 22, wherein the first and second passivating layers are selectedfrom the group including: titanium nitride (TiN); tantaium nitride(TaN); and tungsten nitride (WN).
 24. The capacitor of claim 22, whereinthe lanthanide dielectric film is selected from the group including:Pr2O3; PrSiOx; and PrTiOx.
 25. The capacitor of claim 22, wherein thelanthanide dielectric film includes a layer of PrTiOx and a layer ofPrSiOx.